My son has a 94 GT (same body and rear width) with the 1" spacers. He has 17x9 wheels with 6.25" backset, and runs 275/45 tires without any issues. A little more backset (or removing the spacers) and you could easily run 295s on 10" rims. Quite a bit of room back there.
I've ran 275's for ever on my 95 Mustang GT, 97, 05 and the widest on my 03 Cobra was Nitto 555R 315's with no spacers. 275's will def fit with zero issues. Also i've done 275's up front too. With the 17X9's you can do the Nitto 555R's 315s since they are not a true 315. Other true 315's will not fit a 17X9, like the NT05R's.
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